Circuit breaker tripping system



Marcfi17, 1942. w, sco JR 2,276,675

CIRCUIT BREAKER "DRIPPING SYSTEM v Filed Aug. 11, 1938 5 Sheets-SheetlINVENTOR.

WILLIAM M SCOTT JR.

A TTORNEY.

March 17, 1942.

W. M. SCOTT. JR

ciRcuIT BREAKER TRIPPING SYSTEM Filed Aug. 11, 1938 3 Sheets-Sheet 2F161. La

eespowsws eANqE o|= Ell-"LAY s2 INVENTOR.

NON-

TIME

QE'SPONSWE' EAM E OF= EELAY 52 .rzmmmbu WILLIAM H SCOTT JR.

ATTORNEY.

March 17, 1942. w. M. SCOTT, JR 2,276,675

CIRCUIT BREAKER TRIPPING SYSTEM Filed Aug. 11, 1958 3. Sheets-Sheet 5INVENTOR.

WILLIAM M- SCOTT JR.

A TTORNE Y.

Patented Mar. 17, 1942 UNlTED STATES i ATENT OFFICE 27 Claims.

My invention relates to relay systems and particularly to relay systemsfor controlling circuit breakers in feeder circuits to the third railsor trolley wires, particularly of direct-current railway systems.

In electrical railway systems, power is fed to the trains through atrolley wire or third rail and returns to the power source through thetracks and earth; usually the trolley wire or third rail isseetionalized and each of the sections is connected to a transmissionline along the right of way; substations at the connecting points areprovided with circuit breakers intended to protect the sys tem in eventof occurrence of faults or short circiiits. Particularly in directcurrent systems using steel third rails, the circuit breakers may failto open under some fault conditions and may undesirably open during sometrain-starting conditions; for example, when the fault is remote from afeeder connection, the fault current, because of the relatively highdistributed inductance of the rail and the relatively high resistance ofthe fault circuit, rises slowly to a final magnitude which may be lessthan the magnitude of feeder current when a train is started near thesubstation and when a fault occurs near a feeder connection, the currentin the nearby feeder rapidly rises to tripping magnitude and its circuitbreaker opens but the fault may still be fed from a more remote feederin which the feeder current rises slowly to a, magnitude less than thatnormal for train-starting.

In accordance with my invention, the tripping systems for feeder circuitbreakers discriminate between fault currents and train-starting currentsirrespective of the location of the faults and of the trains duringtheir starting: more particularly, the tripping system for a feedercircuit breaker includes a tripping magnet or relay which trips thecircuit breaker when a slowly rising current attains a magnitudecorresponding with the feeder current under distant fault conditions anda relay responsive, when the rate of rise of feeder current issubstantially equal to or greater than the minimum rate of rise offeeder current under starting conditions, to provide, or modify, a shuntcircuit for the tripping magnet or relay or to vary the bias upon thearmature of the tripping magnet or relay and so preclude tripping of thebreaker upon rapid rise of feeder current unless the increase in feedercurrent attain a magnitude in excess of the maximum increase of feedercurrent under starting conditions; preferably, the tripping current isderived from a current transformer whose primary is traversed by thefeeder current.

In accordance with another aspect of my inven tion, means are providedto enable the tripping system to distinguish between rapid increase andrapid decrease of feeder current and to provide for tripping only whenthe feeder current is rising; to that end there is included in thetripping system of one modification, an asymmetric conductor, orrectifier, preferably connected in shunt to the winding of the trippingmagnet or relay to divert from it at least a substantial part of thecurrent from the transformer secondary when that current is due todecreasing rather than increasing feeder current; when the rectifierused is of a type permitting flow of inverse current, the trippingmagnet or relay is preferably provided with an auxiliary coil so poledand proportioned that the forward current through the rectifier andtraversing the auxiliary coil produces a magneto-motive force inopposition to, and preferably substantially equal to, the magneto-motiveforce developed by the tripping coil: in another modification, thetripping magnet or relay is polarized to discriminate between increaseand decrease of the feeder current.

More particularly, in some forms of my invention, provision is madetemporarily to de-sensitize the tripping magnet or relay during closureof the circuit breaker to preclude tripping in response to an inrush ofcurrent occurring the instant the feeder circuit is first completed; ina preferred arrangement, the tripping magnet or relay, during closure ofthe circuit breaker, is shunted by a resistance of suitably lowmagnitude which is cut out of circuit after the circuit breaker hasclosed.

My invention further resides in the features of combination andarrangement hereinafter described and claimed.

For an understanding of my invention, reference is made to theaccompanying drawings, in which:

Figs. 1, 2 and 3 diagrammatically illustrate relay systems forcontrolling circuit breakers;

Fig. 1a discloses curves referred to in discus sion of the operatingcharacteristics of the tripping systems herein described;

Fig. 4 diagrammatically illustrates a distribution system with provisionfor disconnecting all feeder circuits from a fault;

Fig. 5 diagrammatically illustrates a modification of Figs. 1, 2 and 3which provides for temporary desensitization of the tripping systemduring closure of the circuit breaker;

Fig. 6 illustrates a modification in which the tripping relay ispolarized;

Figs. 7 and 8 illustrate further modifications in which the armatures ofrelays controlling tripping of a circuit breaker are mechanicallycoupled;

Fig. 9 illustrates a further modification in which a voltage coilprovides a bias for the armature of the tripping magnet.

Referring to Fig. 1 which discloses a system for controlling thetripping of circuit breaker B in a feeder P, which may be one of manysimilarly protected feeders connected to the third rail or trolley wireL, the series transformer 'I is connected in the feeder in series withthe contact structure C of the circuit breaker and the direct currentgenerator G, one of whose terminals is connected through the breaker tothe feeder F and the other of whose terminals is connected to the returncircuit, or ground E, usually formed by the car rails. Preferably themagnetic circuit or core of the transformer is provided with an air gapto prevent saturation during flow of heavy currents and to enable it torespond to current surges even when heavily loaded. When there is anincrease or decrease in magnitude of the current traversing the feederthere is produced by the transformer T a current whose polarity dependsupon the sense of change (increase or decrease) of the feeder current,and

whose magnitude is substantially proportional to the change in magnitudeof the feeder current.

The secondary voltage of the transformer is impressed upon the terminals1, 2 of the tripping magnet or relay TR. whose tripping coil 0 is woundupon the core structure I8, l9 preferably provided with an air gap toprevent magnetic saturation under all conditions of operation. Thearmature 4 of relay TR biased as by spring 5 against adjustable stop 6,may either directly trip the breaker B, as by tripping latch I, orequivalent, or may indirectly effect tripping of the breaker as byclosure of the circuit of a tripping coil TC (Figs. 3 and 6 to 8).

In shunt to the operating coil 0 of the tripping relay TR are connectedin series the resistance R, preferably adjustable as by contact 8, andthe winding S of a relay SR. The resistance R and coil S provide inshunt to the operating coil 0 a path whose reactance is materially lessthan that of coil 0; by selection or adjustment the resistance of coil 0is materially less than that of resistance R and the inductance of coil0 is high compared to the inductance of coil S.

When, under conditions hereinafter discussed, the current through relaySR, attains sufficiently high value, its armature 9 closes the contacts[0, ill to shunt all or part of the resistance R, depending upon thesetting on contact I I, and so reduces the impedance of the shunt pathR, S for the operating coil 0 of relay TR. In other words, when therelay SR. responds to close its contacts, an increased percentage of thetotal current from the series transformer flows through the lowreactance path R, S and a decreased percentage flows through coil 0 ofthe tripping relay TR.

The operating characteristics ofthe tripping system of Fig. 1 and infact of all the modifications herein described can best be understoodfrom discussion of Fig. 1a, in which curves a and b are respectivelyexemplary of the rising feeder current when a train exemplified in Fig.1 by locomotive LC, is started near the feeder connection to third railand when a train is started at a more distant point, for example midwaybetween two end feeders of a third-rail section, and in which curves 0,d and e are respectively exemplary of rising feeder currents when afault occurs near a feeder connection, when a fault occurs at a remotepoint, for example at the other end of a third rail section, and when afault occurs at an intermediate point.

A significant relation shown by curves 1) and (Z is that the rate ofrise of feeder current under end-fault conditions is less than the rateof rise of feeder current during mid-section starting conditions. In thelatter case, the rate of rise of feeder current is sufficiently high tocause response of relay SR and close its contacts it, 23; with contactsIll, [0 closed, the tripping magnet TR does not respond unless theincrease in feeder current corresponds With I (Fig. 1a) materiallygreater than the increase in feeder current Ii occurring duringmid-point starting. In the former case, the rate of rise of feedercurrent is insufficient to effect response of relay SR and therefore thetripping magnet effects tripping of the circuit breaker for an increaseI2 in feeder current suitably greater than the increase due tomid-section starting. In brief, when the rate of rise of the feedercurrent is less than that of a curve, not shown, whose tangent is II,which latter is somewhat less steep than the tangent to curve I) at itspoint of greatest curvature, the tripping magnet TR. responds to anincrease 12 in feeder current which is greater than the increase II infeeder current due to mid-section starting and when the rate of rise offeeder current is greater than that of a curve whose tangent is IT therelay SR responds to divert current from coil 0 of the tripping magnetso that it does not respond unless or until th increase in feedercurrent attains a magnitude I suitably higher than the increase I3 infeeder current due to nearby starting yet sufficiently lower than theultimate increase in feeder current otherwise occurring in event of anearby fault adequately to protect the sub-station equipment.

To summarize, the relay SR discriminates b tween the rate of rise offeeder current due to end faults and the rates of rise of feeder currentdue to less remote faults and to all starting conditions. Within thesector marked responsive range of relay SR which comprehends allfeeder-current increase curves whose tangents ar steeper than IT, thetripping system ensures protection against nearby and intermediatefaults without needless tripping during train-starting by tripping onlwhen the feeder current increase corresponds in magnitude with I,whereas within the sector marked Non-responsive range of relay SR thetripping system ensures protection against end faults without needlesstripping during train-starting by tripping when the feeder currentincrease corresponds in magnitude with I2.

The tripping system as thus far described is incapable of distinguishingbetween transformer current due to decrease of the feeder current andtransformer current due to increase of feeder current and thereforethere is the possibility the circuit breaker may trip under conditionsof rapid decrease of feeder current and so interrupt the power whenthere exists no need to do so. This unnecessary tripping of the breakermay be prevented by connecting a rectifier K across the operating coil 0of tripping relay TR and poling it to pass current in its forward or lowresistance direction when the feeder current is decreasing, thus then toserve as a low impedance shunt preventing the current in operating coil0 of magnet TR. from attaining a magnitude sufficient to trip thecircuit breaker.

When the rectifier or asymmetric conductor is of type permitting flow ofsubstantial inverse current, for example a copper, copper-oxiderectifier, the relay TR is preferably provided with an auxiliary coil Hand the rectifier K is connected across, or in series with, the twocoils H and O which are so relatively poled and proportioned that whenthe current flows in the forward direction through the rectifier the netmagneto-motive-force of the two coils is negligible and insufiicient toeffect tripping movement of armature 4 even for rapid decrease inmagnitude of the feeder current.

In the relay system of Fig. 1, closure of the relay contacts l0, leffects a reduction of the impedance of the shunt path S, R bydecreasing the effective magnitude of the resistance R. Alternatively,or in addition, the closure of contacts l0, It] may be utilized toreduce the effective reactance of the shunt circuit: for example, asshown in Fig. 2, the coil S may be provided with a multiplicity of tapsconnected to the points 12 of a switch whose relatively movable contactl3 is connected to one of the relay contacts II). By suitably varyingthe position of the contact I l and/or contact l3, there can be obtainedany desired change in magnitude of the impedance of the shunt path S, Rwhen contacts [0, ll) are closed, and with establishment of any desiredrelation of the resistance to the reactance of this path. However, thetaps are so arranged that the smallest number of turns provided betweencontact l3 and the upper terminal of coil S is effective to hold therelay armature 9o against its pole after it has been attracted thereto.

Further to enhance the ability of the relay or tripping system todistinguish between rates of rise of feeder current associated withnormal starting operations and short circuits, the relay SR (Fig. 2) maybe provided with an auxiliary coil A in series with the operating coil 0of the relay TR. Thus there is imposed upon the armature 9a of the relaySE, a variable biasing effect whose magnitude is determined by themagnitude of current through the operating coil 0 of the tripping relay.For rapid changes in magnitude of the feeder current, and therefore ofthe secondary current of transformer T, the inductive reactance of thecurrent path A, O is large and the current through the shunt circuit S,R more rapidly approaches the value for which the armature 9a isattracted to close contacts l0, l0. When, however, the rate of currentrise is materially lower, the distribution of current between the twopaths is so changed that a greater proportion than before flows throughthe circuit A, O and, in addition, the increased biasing effect of coilA upon the armature 9a requires a greater current through coil S thanbefore to effect movement of the armature 9a.

The movement of the armature 4 of the tripping coil TR may be utilizeddirectly to trip the circuit breaker, as in Fig. 1, or, as shown in Fig.3, the armature when in its attracted position may engage contacts [4 toclose the circuit of a tripping coil TC thus indirectly to effecttripping of the feeder circuit breaker B.

The operating power of the tripping armature 4 may be increased at themoment of its initial movement by causing it to open the shunt path S, Rso that a greater part or all of the current of transformer T traversesthe operating coil O of the tripping relay; the armature 4 may have alost motion connection to the contact member 15 which normally bridgesthe contacts 16, I6 to complete the shunt path S, R.

Preferably the relay TR is so constructed that the armature 4 does notengage the pole pieces in its innermost position, thus to precludepossibility of the armature sticking to the pole pieces. To insure highinductance of the operating coil circuit there may be provided themagnetic shunt element I! which, in the arrangement particularly shown,is an extension of the core member I8. To introduce greater time laginto the operation of the armature 4, one or more copper rings SC, orequivalent, may be disposed about that end of either of the core membersl8, l9 nearest to the armature 4.

The relay system shown in Fig. 3 is the same as that shown in Fig. 2except that relay SR is provided with an additional coil M in serieswith the rectifier K across the terminals of the coils O, H of thetripping relay TR. The purpose of this coil is to ensure operation ofthe relay SR when the current from the transformer is of the sense orpolarity corresponding with a rapid decrease in magnitude of the feedercurrent. The closure of the contacts l0, ID of the relay SR diverts moreof the current through the shunt path and so reduces the load on therectifier K. When the polarity of the transformer current is reversed, amaterially smaller portion of it flows through the coil M because of theasymmetric conductivity of the rectifier and thus, when the feedercurrent is increasing, coil M has little or no effect upon the operatingcharacteristics of the relay SR.

The systems previously described particularly apply to protection of thefeeders from two substations supplying power to a common distributionline or section thereof but in many systems there are more than two substations spaced along the right of way at various suitable intervals tosupply a common load circuit. When the short circuit or fault occursbetween two substations their circuit breakers will open as previouslydescribed, but in systems where the trolley wire or third rail iscontinuous, power will be fed to the fault from the sub-station orsub-stations beyond those protected by tripping of the circuit breakers.For example, referring to Fig. 4, stations #1, 2 and 3 may be protectedby relay systems similar to any of the types herein described. When afault occurs at the point Z, for example, between stations #2 and #3,the feeder breakers B2, B3 are tripped asabove described, but the rateof change of current in feeder Fl at more remote station #1 may be soslow because of the inductance of the long circuit from the connectionof feeder F! to the fault Z that breaker BI does not open and it wouldnot be possible to adjust the relay system to trip under thiscircumstance without so setting it that it would trip under normalstarting or switching operations. To ensure tripping of the breaker BI,and of other circuit-breakers still more remote from the fault, thefault is in effect shifted along the affected section L to cause thetripping of the breakers in all feeders supplying that section; moreparticularly, each of the breakers, or at least each of thoseintermediate the ends of the section, is provided with auxiliarycontacts which upon opening of the breaker produce an artificial orintentional fault to increase the current through the adjacent feeder atsuch rapid rate that its circuit breaker is in turn tripped.Specifically, in the particular example shown in Fig. 4, when thecircuit breaker B2 opens it closes the auxiliary contacts 20, 20 toeffect energization of a relay 2| whose contacts 22 thereupon move tocomplete an artificial fault circuit from the line to ground adjacentstation #2. Preferably the artificial fault circuit so completed mayinclude a resistance Rl to limit the current through feeder Fl to amagnitude not materially in excess of that required to ensure trippingof circuit breaker Bi. Closure of contacts 22 also eifects energizationof holding coil NH to maintain closed the artificial fault circuit untilbreaker Bl is tripped. It is of course to be understood that the circuitbreakers at each of the other stations may be similarly equipped toshift a fault along until all sub-stations feeding that fault have beendisconnected. It is not necessary that the sub-stations or feeders nearthe ends of a section be so equipped because their circuit breakers willrespond to any fault between them and the next sub-station.

The fault-shifting arrangement disclosed in Fig. 4 is claimed in myco-pending application Serial No. 344,851, in part a continuationhereof, filed July 11, 1940.

When a feeder circuit is completed by closure of its circuit breaker,the rate of change of feeder current may be such that the relay systemsthus far described effect tripping of the breaker even though onlynormal load conditions exist. To prevent this, the secondary of thetransformer T may be shunted, as by resistance TS of suitably lowmagnitude, until after the circuit breaker has closed the feedercircuit. Referring to Fig. 5, when the circuit breaker B is open itsauxiliary contact 2Q is in engagement with contacts 23 to connectresistance TS in shunt to the secondary of transformer T and thisengagement is maintained until after the movable contact C of thecircuit breaker engaged the stationary contacts to complete the feedercircuit. After such engagement and during the final increment of closingmo einent of contact C, the contact 24 is, in any suitable manner,pushed away from contacts 2Z3, to open the shunt circuit including theresistance TS. Thus during the initial surge of feeder current, therelay system is de-sensitized but immediately after the feeder circuitis closed its sensitivity is restored for normal operation as previouslydescribed in connection with Figs. 1 to 4.

The circuit breakers in all modifications are preferably of thetrip-free type, for example as disclosed in my Patent $1 2,625,781, inwhich event, the resistance T8 of Fig. 5 is of such magnitude thatnotwithstanding its shunting effect upon coil 0, the circuit breakerwill trip if, during its closure and before disengagement of contact 24from contacts 23, there exists a fault near the feeder connection.

In the systems of Figs. 1 to 3, a rectifier K is used to precludetripping of the breaker when the secondary current of transformer T,though of magnitude and rate of change in magnitude sufiicient to effecttripping, is of polarity correspending to a decrease, rather than anincrease, of the feeder current. In the system of Fig. 6, the rectifierK is not used and its aforesaid purpose is obtained by a modifiedconstruction of the tripping relay TEE which replaces tripping relay TRof Figs. 1 to 3. The tripping coil O is wound upon a magnetic shuntelement 3% extending between the legs of the U-shaped core oran elec-..tromagnet whose coil CEis energized by uni directional currentsupplied from battery 3! or other suitable source. When only coil CE isenergized, the electromagnet is incapable of moving armature 4a to closecontacts I4, 14. The coils CE and 0 are so Wound and connected that whenthe current through coil 0 is of polarity corresponding with decrease inmagnitude of the feeder current its magneto-force is of such sense thereluctance of the magnetic shunt 3D is in effect reduced and so evenmore of the magnetic flux is diverted from armature 4a with the resultit is not attracted even though the rate of change of the feeder currentis high. When, however, the current in coil 0 is of polaritycorresponding with an increase in feeder current, themagnetomotive-force produced by coil 0 in effect increases thereluctance of the magnetic shunt 30 and forces a greater proportion ofthe flux through the armature. Therefore, for increases of feedercurrent, the circuit breaker is tripped if those increases are due tofault conditions previously herein discussed.

in the tripping systems thus far described, the trip relay or magnet TRis set to trip at a predetermined flow of current through its operating1 O, and its calibration, insofar as feeder curlb concerned, is ineffect changed by variation of the impedance of a path in shunt to theopera coil. In the modifications shown in Figs.

11.. 8, the calibration of the trip relay to obrate-selective operationis automatically d in another manner; specifically, the bias restrainingmovement of the armature l of the tripping relay TB is varied bymechanically coupling armature A to the armature of the relay 12.Referring to Fig. '7, the armature 4b of re TB. is connected by spring3! to the armature t?) of relay SR Whose normal position is deterirfidedby the centering springs 32, 32. As in the modifications previouslydescribed, the operating or ii of the relay TR has, or is included in, acircult of high inductance and low resistance and is shunted by a pathR, S of high resistance and 1c J inductance. Consequently when thefeeder current is changing at high rate, a greater proportion of thecurrent from the series transformer T passes through the shunt circuitincluding coil S which thereupon moves its i e 5b in such direction asto move the armature .1: further away from the pole pieces it, i 8, thusto require greater current through coil 0 to effect tripping movement ofarmature 4b. At lower rates of change of feeder current the effect c therelay SR upon the position of armature is less, and therefore lesscurrent through coil 0 of the tripping relay is required to effecttripping movement of armature GD.

he relay system, shown in Fig. 8 is similar to i it of Fig. '7 exceptthat the coil S of relay SR energized from transformer TA whose primaryis connected in series with the primary of transfo .er T and the relayTR. Because the secondary current of transformer TA is a function therate of change of the secondary current normally open switch and asoiu'ce of current, a

battery for example, across the terminals of the coil or in thosesystems having an auxiliary tripping coil TO, the manually controlledswitch may be connected across contacts l4, M of the tripping relay.

The modification shown in Fig. 9 is similar to preceding figures,particularly Fig. 1, with the addition there is imposed upon thearmature A of the tripping magnet or relay TR, as by coil UV, preferablyin series with a current-limiting resistor RL, a restraining actionwhose magnitude is a function of the voltage between the third rail, orequivalent, and ground. Thus it is ensured the circuit breaker will'tripif a relatively small increase of current occurs while the line voltageis substantially below normal. During existence of very heavy load, forexample during simultaneous starting of several trains in the samesection, particularly when they are also drawing current for heating andlighting, the sub-station may be overloaded and have little reservecapacity to deliver current to a fault or short circuit. Under theseconditions, the voltage is below normal and a fault, taxing the stationbeyond its limit, would increase the feeder current by only a relativelysmall amount but would cause a substantial drop in voltage and thereforesubstantial reduction in the restraining action of coil UV. Consequentlyunder such conditions, the operating characteristic of the relay systemis so modified, the armature 4 operates to effect tripping of thecircuit breaker B when a fault occurs even though the additional feedercurrent due to the fault may be relatively small.

What I claim is:

1. A tripping system for a circuit breaker comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker energized from the secondary of said transformer, animpedance vari able to modify the energization of said device from saidsecondary, and electromagnetic means energized from said transformer andhaving armature structure movable to vary said impedance so to vary thesensitivity of said electromagnetic device to changes in magnitude ofsaid current as a function of the rate of change of said current.

2. A tripping system for a circuit breaker comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker having a winding energized from the secondary of saidtransformer, and a current path in shunt to said winding including inseries resistance of magnitude materially greater than the resistance ofsaid winding and reactance whose magnitude is materially less than thereactance of said winding.

3. A tripping system for a circuit breaker comprising a seriestransformer whos primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker having a winding energized from the secondary of saidtransformer, a current path in shunt to said winding includingresistance materially higher than the resistance of said winding and arelay coil whose inductance is materially less than the inductance ofsaid winding, an armature for said relay coil, and relaycontactsoperated by said armature to decrease the impedance of said shunt pathwhen the current through said relay coil attains a predeterminedmagnitude.

4. A tripping system for a circuit breaker comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker having a winding energized from the secondary of saidtransformer, a current path in shunt to said winding includingresistance materially higher than the resistance of said winding and arelay coil whose inductance is materially less than the inductance ofsaid winding, an armature for said relay coil, and relay contactscontrolled by said armature to decrease the effective magnitude of theresistance of said shunt path when the current through said relaycoil'attains a predetermined magnitude.

5. A tripping system for a circuit breaker comprisign a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker and whose winding is. energized from the secondary ofsaid transformer, a current path in shunt to said winding includingresistance materially higher than the resistance of said winding and arelay coil whose inductance is materially less than the inductance ofsaid winding, an armature for said relay coil, and relay contactscontrolled by said armature to decrease the effective inductance of saidcoil when the current through it attains a predetermined magnitude.

6. A tripping system for a circuit breaker comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for effecting tripping of saidcircuit breaker having a winding energized from the secondary of saidtransformer, a current path in shunt to said winding includingresistance materially higher than the resistance of said winding and arelay coil whose inductance is materially less than the inductance ofsaid winding, an armature for said relay coil, and relay contactscontrolled by said armature to change in magnitude the inductance andresistance of said shunt path when the current through said coil attainsa predetermined magnitude.

'7. A relay system for controlling a circuit breaker comprising atransformer Whose primary is in series with the circuit breaker, anelectromagnetic device for tripping said circuit breaker energized fromthe secondary of said transformer, and an asymmetric conductor in shuntto said device to divert therefrom a substantial part of the currentfrom said secondary for one sense of change in magnitude ofuni-directional current traversing said secondary.

8. A relay system. for controlling a circuit breaker comprising atransformer whose primary ,is in series with the circuit breaker, anelectromagnetic device for tripping said circuit breaker having awinding energized from the secondary of said transformer, and a circuitin shunt to said winding comprising an asymmetric conductor and a secondwinding of said device.

9. A relay system for controlling a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnetic device for tripping said circuit breaker having awinding energized from the secondary of said transformer, and a circuitin shunt to said winding comprising a rectifier, of the type permittingflow of inverse current, and a second winding of said device, saidwindings being so poled and proportioned that their resultant magneticeffect issmall during flow of forward current through said rectifier.

A tripping system for a circuit breaker comprising a series transformerWhose primary is traversed by current through the circuit breaker, anelectromagnetic device for effecting tripping of said circuit breakerhaving a winding energized from the secondary of said transformer, asecond electromagnetic device having a winding whose inductance ismaterially less than the inductance of said first-named winding, acurrent path in shunt to said first-named winding comprising aresistance connected in series with said second-named winding, armaturestructure controlled by the current through said second-named winding tovary the impedance of said path, and a winding in series with saidfirst-named winding for opposing movement of said armature structure inresponse to current through said second-named winding.

11. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnetic device for eifecting tripping of said circuit breakerhaving a winding energized from the secondary of said transformer, and asecond electromagnetic device having windings connected respectively inshunt to and in series with said first-named winding and having armaturestructure responsive to the cliiferential effect of its windings to varythe impedance of a current path in shunt to said first-named winding.

12. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker and asource of direct current, an electromagnetic device for efiectingtripping of the circuit breaker having a Winding energized from thesecondary of said transformer, a relay for controlling the impedance ofa path in shunt to said winding; a path in shunt to said windingcomprising an asymmetric conductor, and means for ensuring operation ofsaid relay to reduce the current through said coductor for one sense ofchange of the primary current of said transformer comprising a windingof said relay connected in series with said conductor.

13. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnetic device for efiecting tripping of the circuit breakerhaving a winding energized from the secondary of said transformer, anasymmetric conductor in shunt to said winding, and a relay forcontrolling the impedance of a path in shunt to said winding, said relayhaving a winding included in said path, a winding in series with saidasymmetric conductor, and a winding in series with said first-namedwinding.

14. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnetic device for effecting tripping of the circuit breakerhaving a winding energized from the secondary of said transformer and anauxiliary winding, an asymmetric conductor, and a relay for controllingthe impedance of a path in shunt to said first-named winding, having awinding included in said path, a winding in circuit with said auxiliarywinding and said asymmetric conductor, and a winding in series with saidfirstnamed winding.

15. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnet having a winding energized from the secondary of saidtransformer and an armature whose movement effects tripping of saidcircuit breaker, and means for controlling the impedance of a path inshunt to said winding comprising a relay which has contact structuremovable to vary said impedance and which is deenergized upon trippingmovement of said armature effectively to increase the energization ofsaid electromagnet.

16. A relay system for tripping a circuit breaker comprising atransformer whose primary is in series with the circuit breaker, anelectromagnet having a winding energized from th secondary of saidtransformer and an armature whose movement effects tripping of saidcircuit breaker, and means for controlling the impedance of a path inshunt to said winding comprising a relay whose winding is included insaid path in series with contacts separated by said armature during itstripping movement.

17. In a tripping system for a direct-current circuit breaker, means forprecluding tripping of the breaker upon decrease in magnitude of thefeeder current, and means for precluding tripping of said breaker whenthe rate of change of current in sense and of magnitude otherwiseeffecting tripping is due to closure of the breaker.

18. A tripping system for a circuit breaker having a latch for holdingits contact structure in closed circuit position comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for tripping said latch energizedfrom the secondary of said transformer, and means operable duringclosing of said circuit breaker temporarily to de-sensitize the systemuntil appreciably after resetting of said latch and so preclude trippingof the circuit breaker by that rapid change of said current incident toclosure of the ircuit breaker under normal load conditions.

19. A tripping system for a circuit breaker having a latch for holdingits contact structure in closed circuit position comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device for tripping said latch energizedfrom the secondary of said transformer, and electrical desensitizingmeans controlled by said circuit breaker and operable during closingmovement thereof to prevent said transformer from energizing said devicesumciently to eiTect tripping of said latch until after occurrence ofthe initial surge of current incident to closure of the circuit breakerunder normal load conditions.

20. A tripping system for a circuit breaker comprising a seriestransformer whose primary is traversed by current through the circuitbreaker, an electromagnetic device energized from the secondary of saidtransformer, a de-sensitizing resistance connected in shunt to saiddevice during closure of said circuit breaker, and switch ing meansoperable after initial engagement of the circuit breaker contacts todisconnect said resistance after initiation of flow of said current byclosure of said circuit breaker.

21. A tripping system for a circuit breaker comprising a seriestransformer Whose primary is traversed by current through the circuitbreaker, an electromagnetic device energized from the secondary of saidtransformer upon rapid change in magnitude of the current traversingsaid circuit breaker, and switching means in circuit with said deviceand operable during initial engage ment of the circuit breaker contactstemporarily to preclude energization of said device to extent sufficientto effect tripping of said circuit breaker by that rapid change ofcurrent incident to closure of the circuit breaker under normal loadconditions and operable after said initial engagement to restore normalrelation between the energization of said device and the secondarycurrent of said transformer.

22. In an electrical railway system comprising a third rail or trolleywire, a feeder connected thereto, and a circuit breaker in said feeder,a relay system for controlling tripping of said circuit breaker, withdiscrimination between feeder currents due to short circuits and thosedue to train-starting comprising a transformer whose primary istraversed by uni-directional current of magnitude corresponding withchanges in magnitude of the feeder current, an electromagnetic devicefor effecting tripping of said circuit breaker having a windingenergized from the secondary of said transformer, a current path inshunt to said winding including resistance materially greater than theresistance of said winding and a relay coil whose inductance ismaterially less than the inductance of said winding, an armature forsaid relay coil, and relay contacts controlled by said armature todecrease the effective impedance of said shunt path when the currentthrough said relay coil attains a predetermined magnitude.

23. In an electrical railway system comprising 0 a third rail or trolleywire, a feeder connected thereto, and a circuit breaker in said feeder,a relay system for controlling tripping of said circuit breaker, withdiscrimination between feeder currents due to short circuits and thosedue to l train-starting comprising a transformer whose primary istraversed by uni-directional current of magnitude corresponding with themagnitude of the feeder current, an electromagnetic device for effectingtripping of said circuit breaker hav- 24. A tripping system for adirect-current circuit breaker comprising a series transformer whoseprimary is traversed by direct-current through said circuit breaker, anelectromagnetic device for tripping said circuit breaker energized fromthe secondary of said transformer, and a relay for varying thesensitivity of said device in accordance with the rate of change of saiddirect-current energized from said transformer and having contactstructure in circuit with said device.

25. A tripping system for a circuit breaker comprising means fortripping said circuit breaker upon occurrence of predetermined increaseof current through the circuit breaker, and means for altering inaccordance with rate of change of said current the magnitude of itsincrease required to effect tripping of the circuit breaker by saidfirst-named means comprising a relay the position of whose contactstructure is different for different rates of change of said current tovary the relation between the energization of said tripping means andthe magnitude of said current.

26. A system comprising a third rail or trolley wire, two feedersconnected thereto at substantially spaced points, a circuit breaker ineach of said feeders, and means for effecting tripping of each of saidcircuit breakers upon occurrence of a fault along said rail or wire nearor remote from aforesaid connection thereto of its feeder and forprecluding tripping of either circuit breaker upon train-startinganywhere between said points comprising for each of said circuitbreakers a transformer whose primary is in the associated feeder, anelectromagnetic device for effecting tripping of the circuit breakerhaving a winding energized from the secondary of said transformer, and acurrent path in shunt to said winding including in series reactancewhose magnitude is materially less than the reactance of said windingand resistance of magnitude materially greater than the resistance ofsaid winding.

27. A railway system comprising a third rail or trolley wire, aplurality of feeders connected thereto at substantially spaced points, acircuit breaker in each of said feeders, and relay systems forcontrolling tripping of said circuit breakers with discriminationbetween feeder currents due to short circuits and those due to trainstarting adjacent said points each comprising means precluding trippingof the associated circuit breaker upon decrease in magnitude of itsfeeder current, and means for precluding tripping of the associatedcircuit breaker when the rate of change and magnitude of its feedercurrent otherwise effecting tripping is due to a reclosure of thecircuit breaker.

WILLIAM M. SCOTT, JR.

